Semiconductor wafers that are manufactured into integrated circuits including computer chips are subjected to numerous steps during processing in various pieces of processing equipment. The wafers must be transported from workstation to workstation and often must be temporarily stored in order to accommodate the necessary processing steps. Moreover, the wafers must sometimes be transported or shipped from a wafer manufacturing facility to another site where they are further processed. This is often accomplished by using substrate containers.
Many operational performance requirements are associated with such containers. Generally, such containers need to have an optimal combination of strength, robustness, weight, tolerance control, and cost effectiveness. They may be transported by overhead machinery, they may be washed and reused, they may be opened and closed hundreds of times, and they may be loaded and unloaded hundreds of times.
The containers used for storing 300 mm wafers in between processing steps are known as FOUPs (Front Opening Unified Pods) and the containers conventionally used for shipping 300 mm wafers between facilities are known as FOSBs (Front Opening Shipping Boxes). FOUPs and FOSBs each have a shell with an open interior and shelves in the shell for holding a spaced stack of wafers. Kinematic coupling is provided on the bottom for precisely interfacing with equipment. A front opening in the shell receives a door. The door has a seal to hermetically seal to the shell and a latch mechanism to secure the door in the shell.
Almost all of the components, with the exception of fasteners in some brands, are formed of injection molded polymeric components. Most manufacturers have avoided metal fasteners and metals entirely where possible in wafer containers due to contamination concerns. The substrate containers formed entirely or substantially of polymers have proven to be cost effective and are universally used in the semiconductor industry.
However, polymer-based containers, particularly wafer containers have proven to have certain drawbacks that have to be managed. For example, as semiconductors have become larger in scale, that is, as the number of circuits per unit area has increased, and as wafers have become larger, contaminants have become more of an issue. Contaminants may be particles or airborne molecular contaminants (AMC's) including VOC's (volatile organic compounds). Elimination of metals and use of specialty polymers and other means have addressed the particle contaminant issues. With respect to AMC's, polymers have a tendency to absorb and release moisture and other AMC's. Continual purging of containers has offered a partial solution but purging is not always available, such as when wafers are shipped.
Further, wafers being manufactured into integrated circuits are also sensitive to electrostatic discharge. Electrostatic dissipation (“ESD”) of components involved in handling and storing semiconductor substrates is often required or desired. Conventional polymers do not provide this characteristic and additives and/or special formulations must be utilized. This raises the cost of the polymers and can add to contamination issues as well as changing the molding and other characteristics of the polymers.
Moreover, injection molding containers with the large expanses of polymer walls require precisely controlled wall thickness, process controls, and often supplemental structure for strength, shape stability and dimensional stability. That is, wall thicknesses cannot vary dramatically in different portions of, for example the shell, as cooling after molding will typically cause undesired/uneven shrinkage and shape deformation. Even where there are very tightly controlled processes, molds for polymer products have to be over sized to provide the desired size of the final polymer component, which will be dimensionally different than the mold. Thus, the larger expansive components, such as the shells in FOUPs and FOSBs, have uniform wall thicknesses throughout. Additionally, thin polymer walls are fragile. Drawing a vacuum in polymer containers is generally not considered practical. However, certain polymers have characteristics that make them desirable for substrate containers, particularly containers for larger substrates, such as the FOUPs and FOSBs; these polymers, such as fluoropolymers, polyetheretherketones, and liquid crystal polymers, have low particle generation characteristics and reduced VOC absorption rates, but, can be very difficult to mold. The molding issues discussed above, are exacerbated for these polymers.
FOUPs and FOSBs are manufactured in conformance with standards set forth by the industry standards group SEMI (Semiconductor Equipment and Materials International). These standards provide very tight tolerance location requirements for surfaces and features. Molding inaccuracies such as discussed above can render finished molded product as unusable.
SEMI standards also provide positioning of a robotic flange on the top of the FOUPs and FOSBs. The robotic flange is centered coaxially with the center of the spaced stack of wafers contained in the containers. Considering the conventional uniform wall thicknesses of the polymer molded shell, and the additional forward positioned polymer due to the presence of the door frame and door at the forward part of the container, when such containers are supported and transported by their robotic flange, the forward portion of the container is much heavier than the rearward portion. This shifts the center of gravity forward imparts is a moment to the flange and transport system connection urging the front of the containers downward when they are suspended from above. Such can have a detrimental effect, particularly during overhead transport of the containers, causing, for example, high stress points on the robotic flange and stress on the transport system, potentially leading to failure of the connection or transport anomalies. One known way to address this issue is with separate ballast weights added rearwardly on the containers. (See U.S. Pat. No. 8,881,907.)
Generally during transport and handling, it is desirable to minimize vibration and any shock events as such may tend to generate and/or launch particles within the substrate container. Any improvement of such vibration and shock absorption and/or minimization of same would be welcome.
To the extent that these problems may be overcome and performance improved while still providing a cost effective solution would be welcomed by the semiconductor processing industry.